The invention generally relates to the field of mechanical locking of floorboards. The invention relates to an improved locking system for mechanical locking of floorboards, a floorboard provided with such an improved locking system, and a flooring made of such mechanically joined floorboards. The invention generally relates to an improvement of a locking system of the type described and shown in WO 9426999 and WO 9966151.
More specifically, the invention relates to a locking system for mechanical joining of floorboards of the type having a core and preferably a surface layer on the upper side of the core and a balancing layer on the rear side of the core, said locking system comprising: (i) for horizontal joining of a first and a second joint edge portion of a first and a second floorboard respectively at a vertical joint plane, on the one hand a locking groove which is formed in the underside of said second board and extends parallel with and at a distance from said vertical joint plane at said second joint edge and, on the other hand, a strip integrally formed with the core of said first board, which strip at said first joint edge projects from said vertical joint plane and supports a locking element, which projects towards a plane containing the upper side of said first floorboard and which has a locking surface for coaction with said locking groove, and (ii) for vertical joining of the first and second joint edge, on the one hand a tongue which at least partly projects and extends from the joint plane and, on the other hand, a tongue groove adapted to coact with said tongue, the first and second floorboards within their joint edge portions for the vertical joining having coacting upper and coacting lower contact surfaces, of which at least the upper comprise surface portions in said tongue groove and said tongue.
The present invention is particularly suitable for mechanical joining of thin floating floors of floorboards made up of an upper surface layer, an intermediate fibreboard core and a lower balancing layer, such as laminate flooring and veneer flooring with a fibreboard core. Therefore, the following description of the state of the art, problems associated with known systems, and the objects and features of the invention will, as a non-restricting example, focus on this field of application and, in particular, on rectangular floorboards with dimensions of about 1.2 m*0.2 m and a thickness of about 7-10 mm, intended to be mechanically joined at the long side as well as the short side.
Thin laminate flooring and wood veneer flooring are usually composed of a core consisting of a 6-9 mm fibreboard, a 0.20-0.8 mm thick upper surface layer and a 0.1-0.6 mm thick lower balancing layer. The surface layer provides appearance and durability to the floorboards. The core provides stability and the balancing layer keeps the board level when the relative humidity (RH) varies during the year. The RH can vary between 15% and 90%. Conventional floorboards of the type are usually joined by means of glued tongue-and-groove joints (i.e. joints involving a tongue on a floorboard and a tongue groove on an adjoining floorboard) at the long and short sides. When laying the floor, the boards are brought together horizontally, whereby a projecting tongue along the joint edge of a first board is introduced into a tongue groove along the joint edge of the second adjoining board. The same method is used at the long side as well as the short side. The tongue and the tongue groove are designed for such horizontal joining only and with special regard to how glue pockets and gluing surfaces should be designed to enable the tongue to be efficiently glued within the tongue groove. The tongue-and-groove joint presents coacting upper and lower contact surfaces that position the boards vertically in order to ensure a level surface of the finished floor.
In addition to such conventional floors, which are connected by means of glued tongue-and-groove joints, floorboards have recently been developed which are instead mechanically joined and which do not require the use of glue. This type of mechanical joint system is hereinafter referred to as a xe2x80x9cstrip-lock systemxe2x80x9d, since the most characteristic component of this system is a projecting strip which supports a locking element.
WO 9426999 and WO 9966151 (owner Valinge Aluminum AB) disclose a strip-lock system for joining building panels, particularly floorboards. This locking system allows the boards to be locked mechanically at right angles to as well as parallel with the principal plane of the boards at the long side as well as at the short side. Methods for making such floorboards are disclosed in EP 0958441 and EP 0958442 (owner Valinge Aluminium AB). The basic principles of the design and the installation of the floorboards, as well as the methods for making the same, as described in the four above-mentioned documents, are usable for the present invention as well, and therefore these documents are hereby incorporated by reference.
In order to facilitate the understanding and description of the present invention, as well as the comprehension of the problems underlying the invention, a brief description of the basic design and function of the known floorboards according to the above-mentioned WO 9426999 and WO 9966151 will be given below with reference to FIGS. 1-3 in the accompanying drawings. Where applicable, the following description of the prior art also applies to the embodiments of the present invention described below.
FIGS. 3a and 3b are thus a top view and a bottom view respectively of a known floorboard 1. The board 1 is rectangular with a top side 2, an underside 3, two opposite long sides with joint edge portions 4a, 4b and two opposite short sides with joint edge portions 5a, 5b. 
Without the use of the glue, both the joint edge portions 4a, 4b of the long sides and the joint edge portions 5a, 5b of the short sides can be joined mechanically in a direction D2 in FIG. 1c, so that they join in a joint plane F (marked in FIG. 2c). For this purpose, the board 1 has a flat strip 6, mounted at the factory, which strip extends throughout the length of the long side 4a and which is made of flexible, resilient sheet aluminium. The strip 6 projects from the joint plane F at the joint edge portion 4a. The strip 6 can be fixed mechanically according to the embodiment shown, or by means of glue, or in some other way. Other strip materials can be used, such as sheets of other metals, as well as aluminium or plastic sections. Alternatively, the strip 6 may be made in one piece with the board 1, for example by suitable working of the core of the board 1. The present invention is usable for floorboards in which the strip is integrally formed with the core, and solves special problems appearing in such floorboards and the making thereof. The core of the floorboard need not be, but is preferably, made of a uniform material. However, the strip 6 is always integrated with the board 1, i.e. it is never mounted on the board 1 in connection with the laying of the floor but it is mounted or formed at the factory. The width of the strip 6 can be about 30 mm and its thickness about 0.5 mm. A similar, but shorter strip 6xe2x80x2 is provided along one short side 5a of the board 1. The part of the strip 6 projecting from the joint plane F is formed with a locking element 8 extended throughout the length of the strip 6. The locking element 8 has in its lower part an operative locking surface 10 facing the joint plane F and having a height of e.g. 0.5 mm. When the floor is being laid, this locking surface 10 coacts with a locking groove 14 formed in the underside 3 of the joint edge portion 4b of the opposite long side of an adjoining board 1xe2x80x2. The short side strip 6xe2x80x2 is provided with a corresponding locking element 8xe2x80x2, and the joint edge portion 5b of the opposite short side has a corresponding locking groove 14xe2x80x2. The edge of the locking grooves 14, 14xe2x80x2 closest to the joint plane F forms an operative locking surface 11 for coaction with the operative locking surface 10 of the locking element.
Moreover, for mechanical joining of both long sides and short sides also in the vertical direction (direction D1 in FIG. 1c) the board 1 is formed with a laterally open recess 16 along one long side (joint edge portion 4a) and one short side (joint edge portion 5a). At the bottom, the recess 16 is defined by the respective strips 6, 6xe2x80x2. At the opposite edge portions 4b and 5b there is an upper recess 18 defining a locking tongue 20 coacting with the recess 16 (see FIG. 2a).
FIGS. 1a-1c show how two long sides 4a, 4b of two such boards 1, 1xe2x80x2 on an underlay U can be joined together by means of downward angling. FIGS. 2a-2c show how the short sides 5a, 5b of the boards 1, 1xe2x80x2 can be joined together by snap action. The long sides 4a, 4b can be joined together by means of both methods, while the short sides 5a, 5bxe2x80x94when the first row has been laidxe2x80x94are normally joined together subsequent to joining together the long sides 4a, 4b and by means of snap action only.
When a new board 1xe2x80x2 and a previously installed board 1 are to be joined together along their long side edge portions 4a, 4b as shown in FIGS. 1a-1c, the long side edge portion 4b of the new board 1xe2x80x2 is pressed against the long side edge portion 4a of the previous board 1 as shown in FIG. 1a, so that the locking tongue 20 is introduced into the recess 16. The board 1xe2x80x2 is then angled downwards towards the subfloor U according to FIG. 1b. In this connection, the locking tongue 20 enters the recess 16 completely, while the locking element 8 of the strip 6 enters the locking groove 14. During this downward angling, the upper part 9 of the locking element 8 can be operative and provide guiding of the new board 1xe2x80x2 towards the previously installed board 1. In the joined position as shown in FIG. 1c, the boards 1, 1xe2x80x2 are locked in both the direction D1 and the direction D2 along their long side edge portions 4a, 4b, but the boards 1, 1xe2x80x2 can be mutually displaced in the longitudinal direction of the joint along the long sides.
FIGS. 2a-2c show how the short side edge portions 5a and 5b of the boards 1, 1xe2x80x2 can be mechanically joined in the direction D1 as well as the direction D2 by moving the new board 1xe2x80x2 towards the previously installed board 1 essentially horizontally. Specifically, this can be carried out subsequent to joining the long side of the new board 1xe2x80x2 to a previously installed board 1 in an adjoining row by means of the method according to FIGS. 1a-1c. In the first step in FIG. 2a, bevelled surfaces adjacent to the recess 16 and the locking tongue 20 respectively cooperate such that the strip 6xe2x80x2 is forced to move downwards as a direct result of the bringing together of the short side edge portions 5a, 5b. During the final bringing together, the strip 6xe2x80x2 snaps up when the locking element 8xe2x80x2 enters the locking groove 14xe2x80x2, so that the operative locking surfaces 10, 11 of the locking element 8xe2x80x2 and of the locking groove 14xe2x80x2 will engage each other.
By repeating the steps shown in FIGS. 1a-c and 2a-c, the whole floor can be laid without the use of glue and along all joint edges. Known floorboards of the above-mentioned type are thus mechanically joined usually by first angling them downwards on the long side, and when the long side has been secured, snapping the short sides together by means of horizontal displacement of the new board 1xe2x80x2 along the long side of the previously installed board 1. The boards 1, 1xe2x80x2 can be taken up in the reverse order of laying without causing any damage to the joint, and be laid again. These laying principles are also applicable to the present invention.
For optimal function, subsequent to being joined together, the boards should be capable of assuming a position along their long sides in which a small play can exist between the operative locking surface 10 of the locking element and the operative locking surface 11 of the locking groove 14. Reference is made to WO 9426999 for a more detailed description of this play. Such a play can be in the order of 0.01-0.05 mm between the operative locking surfaces 10, 11 when pressing the long sides of adjoining boards against each other. However, there need not be any play at the upper edge of the joint edges at the upper side of the floorboards.
In addition to what is known from the above-mentioned patent specifications, a licensee of Vxc3xa4linge Aluminium AB, Norske Skog Flooring AS, Norway (NSF), introduced a laminated floor with mechanical joining according to WO 9426999 in January 1996 in connection with the Domotex trade fair in Hannover, Germany. This laminated floor, which is shown in FIG. 4a and is marketed under the trademark Alloc(copyright), is 7.2 mm thick and has a 0.6-mm aluminium strip 6 which is mechanically attached on the tongue side. The operative locking surface 10 of the locking element 8 has an inclination (hereinafter termed locking angle) of about 80xc2x0 to the plane of the board. The locking element has an upper rounded guiding part and a lower operative locking surface. The rounded upper guiding part, which has a considerably lower angle than the locking surface, contributes significantly to position20 ing of the boards in connection with installation and facilitating the sliding-in of the locking element into the locking groove in connection with angling and snap action. The vertical connection is designed as a modified tongue-and-groove joint, the term xe2x80x9cmodifiedxe2x80x9d referring to the possibility of bringing the tongue groove and tongue together by way of angling.
WO 9747834 (owner Unilin Beeher B. V., the Netherlands) describes a strip-lock system which has a fibreboard strip and is essentially based on the above known principles. In the corresponding product, xe2x80x9cUniclicxe2x80x9d, which this owner began marketing in the latter part of 1997 and which is shown in FIG. 4c, one seeks to achieve biasing of the boards. This results in high friction and makes it difficult to angle the boards together and to displace them. The document shows several embodiments of the locking system. All locking surfaces have an angle that does not exceed 60xc2x0 and the joint systems have no guiding surfaces.
Other known locking systems for mechanical joining of board materials are described in, for example, GB-A-2,256,023 showing unilateral mechanical joining for providing an expansion joint in a wood panel for outdoor use. The locking system does not allow joining of the joint edges and is not openable by upward angling round the joint edges. Moreover the locking element and the locking groove are designed in a way that does not provide sufficient tensile strength. U.S. Pat. No. 4,426,820 (shown in FIG. 4e) which concerns a mechanical locking system for a plastic sports floor, which floor is intentionally designed in such manner that neither displacement of the floorboards along each other nor locking of the short sides of the floorboards by snap action is allowed.
In the autumn of 1998, NSF introduced a 7.2-mm laminated floor with a strip-lock system which comprises a fibreboard strip and is manufactured according to WO 9426999 and WO 9966151. This laminated floor is marketed under the trademark xe2x80x9cFiboloc(copyright)xe2x80x9d and has the cross-section illustrated in FIG. 4b. 
In January 1999, Kronotex GmbH, Germany, introduced a 7.8 mm thick laminated floor with a strip lock under the trademark xe2x80x9cIsilock(copyright)xe2x80x9d. A cross-section of the joint edge portion of this system is shown in FIG. 4d. Also in this floor, the strip is composed of fibreboard and a balancing layer.
During 1999, the mechanical joint system has obtained a strong position on the world market, and some twenty manufacturers have shown, in January 2000, different types of systems which essentially are variants of Fiboloc(copyright), Uniclic(copyright) and Isilock(copyright). All systems have locking surfaces with low locking angles and the guiding, in the cases where it occurs, is to be found in the upper part of the locking element.
Although the floors according to WO 9426999 and WO 99/66151 and the floor sold under the trademark Fiboloc(copyright) exhibit major advantages in comparison with traditional, glued floors, further improvements are desirable mainly in thin floor structures.
The vertical joint system, which comprises locking elements and locking grooves, has two coacting parts, viz. a locking part with operative locking surfaces which prevent the floorboards from sliding apart, and a guiding part, which positions the boards and contributes to the locking element being capable of being inserted into the locking groove. The greater the angular difference between the locking surface and the guiding part, the greater the guiding capacity.
The preferred embodiment of the locking element according to WO 9426999, having a rounded upper part and an essentially perpendicular lower locking surface, is ideal for providing a joint of high strength. The inward angling and snapping-in function is also very good and can be achieved with completely tight joint edges owing to the fact that the strip is bent downwards, whereby the locking element opens and snaps into the locking groove.
The drawback of this design of the locking element is the taking-up function, which is a vital part in most mechanical locking systems. The locking groove follows a circular arc with its centre in an upper joint edge (i.e. where the vertical joint plane intersects the upper side of the floorboard). If the locking groove has a locking angle corresponding to the tangent to the circular arc, below referred to as clearance angle, taking-up can be carried out without problems. If the locking angle is greater than the clearance angle, the parts of the locking system will overlap each other in upward angling, which makes the taking-up considerably more difficult.
Alloc(copyright) (see FIG. 4a) has an aluminium strip with a locking angle of about 80xc2x0 and a clearance angle of about 65xc2x0. The other known systems with strips made integrally with the core of the floorboard have locking angles and clearance angles of 30-55xc2x0 owing to the width of the strip being narrower and the radius of the circular arc being smaller. This results in low tensile strength in the horizontal direction D2 since the locking element easily slides out of the locking groove. Moreover, the horizontal tensile stress will be partly converted into an upwardly directed force which may cause the edges to rise. This basic problem will now be explained in more detail.
When the relative humidity, RH, changes from about 80% in summer to about 20% in winter, the floating floor shrinks by about 10 mm in a normal room. The motion takes place in a concealed manner under the skirting board at the surrounding walls. This shrinkage will move all furniture which exerts a load onto the floor. Tests have shown that if a room is fitted with heavy bookcases along the walls, the joint will be subjected to very high load or tensile stress in winter. At the long side this load may amount to about 300 kg/running meter of joint. At the short side where the load is distributed over a smaller joint width, the load may amount to 500 kg/running meter.
If the locking surfaces have a low locking angle, the strength of the joint will be reduced to a considerable extent. In winter the joint edges may slide apart so that undesirable visible joint gaps arise on the upper side of the floor. Besides, the angled locking surface of the locking element will press the upper locking surface of the locking groove upwards to the joint surface. The upper part of the tongue will press the upper part of the tongue groove upwards, which results in undesirable rising of the edges. The present invention is based on the understanding that these problems can be reduced to a considerable extent, for example, by making the locking surfaces with high locking angles exceeding 50xc2x0 and, for instance, by the locking surfaces being moved upwards in the construction. The ideal design is perpendicular locking surfaces. Such locking surfaces, however, are difficult to open, especially if the strip is made of fibreboard and is not as flexible as strips of e.g. aluminium.
Perpendicular locking surfaces can be made openable if interaction between a number of factors is utilised. The strip should be wide in relation to the floor thickness and it should have good resilience. The friction between the locking surfaces should be minimised, the locking surface should be small and the fibre material in the locking groove, locking element and upper joint edges of the locking system should be compressible. Moreover, it is advantageous if the boards in the locked position can assume a small play of a few hundredths of a millimetre between the operative locking surfaces of the locking groove and the locking element if the long side edge portions of the boards are pressed together.
There are today no known products or methods which give sufficiently good solutions to problems which are related to essentially perpendicular locking surfaces which are at the same time easy to open.
It would be a great advantage if openable locking surfaces could be made with greater degrees of freedom and a high locking angle, preferably 90xc2x0, in combination with narrow strips which reduce waste in connection with working. The manufacture would be facilitated since working tools would only have to be guided accurately in the horizontal direction and the joint would obtain high strength.
To sum up, there is a great need for providing a locking system which takes the above-mentioned requirements, problems and desiderata into consideration to a greater extent than prior art. The invention aims at satisfying this need.
An object of the present invention therefore is to provide a locking system having
(i) locking surfaces with a high locking angle and high strength,
(ii) a horizontal joint system which has such locking surfaces and which at the same time is openable, and
(iii) a horizontal joint system which has such locking surfaces and at the same time comprises guiding parts for positioning of the floorboards.
The invention is based on a first understanding that the identified problems must essentially be solved with a locking system where the locking element has an operative looking surface in its upper part instead of in its lower part as in prior-art technique. When taking up an installed floor by upward angling, the locking surface of the locking groove will therefore exert a pressure on the upper part of the locking element. This results in the strip being bent backwards and downwards and the locking element being opened in the same way as in inward angling. In a suitable design of locking element and locking groove, this pressure can be achieved in a part of the locking element which is closer to the top of the locking element than that part of the locking element which is operative in the locked position. In this way, the opening force will be lower than the locking force.
The invention is also based on a second understanding which is related to the motions during upward angling and taking-up of an installed floor. The clearance angling, i.e. the tangent to a circular arc with its centre where the vertical joint plane intersects the upper side of the floorboard, is higher in the upper part of the locking element than in its lower part. If a part of the locking surface, which in prior-art technique is placed in the lower part of the locking element and the locking groove respectively, is placed in the upper part instead according to the invention, the difference in degree between the locking angle and the clearance angle will be smaller, and the opening of the locking when taking up an installed floor will be facilitated.
The invention is also based on a third understanding which is related to the guiding of the floorboards during inward angling when the floor is to be laid. Guiding is of great importance in inward angling of the long sides of the floorboards since the floorboards have often warped and curved and therefore are somewhat arcuate or in the shape of a xe2x80x9cbananaxe2x80x9d. This shape of a banana can amount to some tenths of a millimetre and is therefore not easily visible to the naked eye in a free board. If the guiding capacity of the locking system exceeds the maximum banana shape, the boards can easily be angled downwards, and they need not be pressed firmly against the joint edge in order to straighten the banana shape and allow the locking element to be inserted into the locking groove. In prior-art locking systems, the guiding part is formed essentially in the upper part of the locking element, and if the locking surface is moved up to the upper part, it is not possible to form a sufficiently large guiding part. A sufficiently great and above all more efficient and reliable guiding is achieved according to the invention by the guiding part being moved to the locking groove and its lower part. According to the invention it is even possible to form the entire necessary guiding in the lower part of the locking groove. In preferred embodiments, coacting guiding parts can also be formed both in the upper part of the locking element and the lower part of the locking groove.
According to a first aspect of the invention, a locking system is provided of the type which is stated by way of introduction and which according to the invention is characterised by the combination that the locking element has at least one operative locking surface which is positioned in the upper part of the locking element, that this operative locking surface is essentially plane and in relation to the plane of the boards has an angle (A) which exceeds 50xc2x0, that the locking groove has at least one locking surface which is essentially plane and which cooperates with said locking surface of the locking element, that the locking groove has a lower inclined or rounded guiding part which guides the locking element into the locking groove by engagement with a portion of the locking element which is positioned above the locking surface of the locking element or adjacent to its upper edge.
The invention concerns a locking system for mechanical joining of floorboards and a floorboard having such a locking system. The locking system has mechanical cooperating means for vertical and horizontal joining of adjoining floorboards. The means for horizontal joining about a vertical joint plane comprise a locking groove and a locking strip which are positioned at the opposite joint edge portions of the floorboard. The locking strip extends from the joint plane and has an upwardly projecting locking element at it free end. The locking groove is formed in the opposite joint edge portion of the floorboard at a distance from the joint plane. The locking groove and the locking element have operative locking surfaces. These locking surfaces are essentially plane and positioned at a distance from the upper side of the projecting strip and in the locking groove and form an angle of at least 50xc2x0 to the upper side of the board. Moreover, the locking groove has a guiding part for cooperation with a corresponding guiding part of the locking element.